Studies are proposed to characterize some specific aspects of the molecular biology of two mycoplasma viruses. These are MVL51, a Group 1 virus, and MVL2, a Group 2 virus. Group 1 viruses are naked bullet shaped particles containing circular single stranded DNA of 2 x 10 to the 6th power daltons. Group 2 viruses are enveloped particles containing DNA. The studies will examine: (1) MVL51 gene products during infection. (2) the virus carrier state, (3) the MVL2 membrane and its relationship to the cell membrane, and (4) the intracellular replicative intermediates produced during MVL2 infection. BIBLIOGRAPHIC REFERENCES: Das, J. and J. Maniloff (1976). Replication of mycoplasmavirus MVL51: Attachment of MVL51 parental DNA to host cell membrane. Proc. Nat. Acad. Sci. USA 73: 1489-1493. Das, J. and J. Maniloff (1976). Replication of mycoplasmavirus MVL51. IV. Inhibition of viral synthesis by rifampin. J. Virol. 18:969-976.